Prevention of Blowout Tests in Large-Diameter Boreholes with Soundless Chemical Demolition Agents and Fracturing Characteristics of Hard Sandstones

Increasing the diameter of the drillhole can facilitate drillhole breakage using soundless chemical demolition agents, but it is prone to cause drillhole blowout, resulting in crushing failure. This paper conducted a blowhole prevention test on a large borehole using the internal insertion cooling pipe method (ICBPM) to test the expansion pressure of cooling pipes with different diameters. During this test, a fracture occurred in a hole with a 75 mm inner diameter in the rectangular sandstone specimens with high strength. It was found that utilizing the ICBPM can effectively hinder the development of blowholes. Expansion and blowhole prevention are optimized with a 0.14 mass ratio of the cooling water to demolition agent and a maximum expansion stress of 49.0 MPa. The guiding effect of the minimum resistance line is significant. In repeated tests, all fissures are distributed in a Y-shape on the free surface where the minimum resistance line is located. The acoustic emission signals from statically fractured hard rock increase abruptly before damage, and the development of rock expansion and fracturing can be obtained through strain monitoring. These results suggest that the ICBPM can reduce the expansion time with a strong crushing effect, satisfying the need to process more crushing projects.